bloodstain evidence may reveal: origin(s) of bloodstain distance of bloodstain from target direction...

Bloodstain EvidenceBloodstain EvidenceMay reveal:May reveal:

• Origin(s) of bloodstain• Distance of bloodstain from target• Direction from which blood impacted• Speed with which blood left its source• Position of victim & assailant• Movement of victim & assailant• Number of blows/shots

1

Liquid BloodLiquid Blood• Physical properties

– viscosity

– surface tension

– specific gravity

• Behaves as a projectile in motion– biology, physics, maths

2

Blood lab 1

• We measured the diameter of blood drops from different heights

• Whiteboard now:– What was the independent variable?– What was the dependent variable?– What type of graph did we use and why?

Surface TensionSurface Tension

• Resistance to penetration & separation• Surface acts to reduce surface area

• Smallest SA to Volume ratio is offered by sphere

3

Dripping BloodDripping Blood

Blood drop grows until Wt (G) > S.T.

Single drop breaks free (teardrop shape)

Surface tension pulls in vertically

Shape settles into sphere (0.05 ml)

Does not break up until impact

And horizontally

Blood trickles downwards

4

Drop size

.

Standard drop size 50ul (0.05ml)

.

Rapid bleeding gives slightly larger drop

Shaking/movementcasts off smaller drops

.

5

Terminal Velocity v Distance Fallen(metric)

Terminal velocity as a function of distance fallen (metric)

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6 7

Fall distance (m)

Ter

min

al v

elo

city

(m

/s)

6

Terminal Velocity v Distance Fallen(imperial)

Terminal velocity as a function of distance fallen (imperial)

0

5

10

15

20

25

30

0 2 4 6 8 10 12 14 16 18 20

Distance fallen (f)

Te

rmin

al v

elo

cit

y (f

/s)

7

Free Falling Blood Droplets

.

50 ul4.6 mm

7.5 m/s

4.2 to5.4 m

0.5 ul2.12 mm

2.4 to 3 m

.4.6 m/s

0.12 ul1.32 mm

0.84 to 1 m

.3.3 m/s

0.06 ul1.1 mm

0.5 to 0.65 m

.2.2 m/s

8

Shape & Size of BloodspotShape & Size of Bloodspot

• Depends mostly on nature of target surface– texture (rough or smooth)– porous or non porous

• Size is related to distance fallen, provided:– standard 50 ul drop of blood

• There is little change in spot diameter beyond a fall distance of 1.2 m

9

Height FallenHeight Fallen

Single drops of blood falling from fingertip onto smooth cardboard from various heights.No change in diameter beyond 7 ft.

Adapted from Introduction to Forensic Sciences,W. Eckert, CRC, 1997

10

Blood Lab 2

• We looked at how different surfaces affect the blood splatter

• Whiteboard now:– What was the independent variable?– Dependent variable?– Control?– What kind of graph did you use and why?

Effect of Target SurfaceEffect of Target Surface

. .... .Spreads out smoothly ST of spreading edge is

broken by irregular surface

11

Experiments with Falling Blood DropletsExperiments with Falling Blood Droplets

blood

dropper

ruler

Terazzo floor

whiteboard

rough paper towel

paper

Fabric (theatre green)

Height

Target Surface

12

Height/Surface

Single drop of blood falling from various heights (m) onto various surfaces

smooth floor paper towel fabric

0.5

1

2

3

0.5

1

2

3

13

Blood Lab 3

• We looked at direction of blood splatter

• Whiteboard now:– What was the independent variable?– Dependent variable?

– CSI video

Blood Lab 4

• We looked at how angle has an effect on blood drops

• Whiteboard now:– Independent and dependent variable?– Name 2 characteristics you noticed of the blood

spatter relative to angle

Angle of Angle of ImpactImpact

90

10

70

2030

60 50 40

Adapted from Introduction to Forensic Sciences,W. Eckert, CRC, 1997

80

Gravitational dense zoneat lower edge

14

Wave Cast-offWave Cast-offDavid Sadler:David Sadler:

.Parent drop

wave cast-off

Tail of wave cast-off points back to parent drop

Tail of elongated stain points in direction of travel

15

Point of ConvergencePoint of Convergence16

Point of ConvergencePoint of Convergence5 ml blood squirted from a syringe from height of 1 m

17

Point of OriginPoint of Origin

length

width

Angle of impact = arc sin W/L

Distance from point of convergence

Hei

ght a

bove

poi

nt o

f co

nver

genc

e

Origin

85 60 45 30

181

Tracing Origin of Tracing Origin of BloodspotsBloodspots

• Point of convergence method– 2 dimensional image

• Point of origin method– adds 3rd dimension to image

• In practice:– use of string & protractor at scene

– use of computer at laboratory

19

Blood SpatterBlood Spatter

• Low velocity (5 f/s, 1.5 m/s)– e.g. free-falling drops, cast off from weapon

• Medium velocity (25 - 100 f/s, 7.5 - 30 m/s)– e.g. baseball bat blows

• High velocity (>100 f/s, 30 m/s)– e.g. gunshot, machinery

20

Herbert Leon MacDonell,

Laboratory of Forensic Science,P.O. Box 1111,Corning,New York,14830,USA

21

Cast-off from WeaponCast-off from Weapon

• First blow causes bleeding• Subsequent blows contaminate weapon with

blood• Blood is cast-off tangientially to arc of upswing

or backswing• Pattern & intensity depends on:

– type of weapon

– amount of blood adhering to weapon

– length of arc

23

Downswing of HammerDownswing of Hammer

24

Cast-off from WeaponCast-off from Weapon

ceiling

25

Overhead swing with bloodied metal bar26

Cast-off Pattern (1/2)Cast-off Pattern (1/2)

27

Cast off Pattern (2/2)Cast off Pattern (2/2)1

2

3

28

Cast off Pattern (2/2) Cast off Pattern (2/2) ? Sequence? Sequence

29

Cast off Pattern (2/2) Cast off Pattern (2/2) ? Sequence? Sequence 1

(4 spots)

2(3 spots)

3(2 spots)

If weapon does not pick up more blood, spatter from subsequent backswings becomes progressively less.In practice weapon picks up more blood with each successful blow.

30

Three overhead swings with hatchet

31

Cast-off & medium velocity spatter32

Cast-off & medium velocity spatter 233

Cast-off PatternCast-off Pattern? Object? Object

34

Cast-off PatternCast-off Patternfrom Handfrom Hand

35

Cast-off pattern from bloodied hand swung in front of target

6” ruler

36

.... ...

..

...

Drip PatternDrip Pattern

• Free-falling drops dripping into wet blood• Large irregular central stain• Small round & oval satellite stains

.. .......

37

Drip 1:Drip 1:

Blood dripping into itself from height of 1 m (8 drops)

38

Drip 2Drip 2

Blood dripping into itself from height of 1 m (8 drops)

39

Dripping onto steps

40

Splash onto vertical surface

6” ruler

10 ml blood thrown 1 m onto a vertical target surface

45

Stamping in blood 1

Area seen in close-up in next slide

46

Stamping in blood Close-up of heel area

47

Stamp 1Stamp 1

Blood pool (10 drops) before stamping

48

Stamp 2Stamp 2

Blood pool (10 drops) after stamping49

Arterial Spurt PatternArterial Spurt Pattern• Blood exiting body under arterial pressure• Large stains with downward flow on

vertical surfaces• wave-form of pulsatile flow may be

apparent

50

Small arterial spurt

spatter

broken pottery

51

Neck incisions (scene)52

Neck incisions

Thyroid cartilage

Probe in carotid artery

‘Hesitation’ injuries

53

Medium Velocity Medium Velocity Blood SpatterBlood Spatter

• Blood source subjected to MV impact– (25 - 100 f/s, 7.5 - 30 m/s)

• Spot diameter: mostly 1 - 4 mm• Blows with weapon (e.g. baseball bat)

54

Medium velocity blood spatter.Point of impact 15 cm in front of vertical target surface

6” ruler

55

Flick 1:Flick 1:

Blood flicked between middle finger & thumb onto a vertical smooth surface from a distance of 15 cm

56

Flick 2:Flick 2:

Blood flicked between middle finger & thumb onto a vertical smooth surface from a distance of 15 cm

57

High Velocity Blood SpatterHigh Velocity Blood Spatter• Blood source subjected to HV impact

– > 100 f/s, 30 m/s

• Fine mist: spot size < 0.1 mm• Small mass limits spread to 1 m• !Some larger droplets reach further• Gunshot

– back-spatter from entry wound– forward spatter from exit wound

• High speed machinery

58

Gunshot: back& forward spatterBloodstained foam held just above target surface.

Back-spatter on entry

Forward spatteron exit

bullet

Bullet passing L to R just above sheet

Bullet enters foam

bullet exits foam

59

Gunshot Back SpatterGunshot Back Spatter

• Arises from entrance wound• Passes back towards weapon & shooter• Seen only at close range of fire• Seen on:

– inside of barrel

– exterior of weapon

– hand, arm, chest of shooter

60

Back spatter on steadying

hand

61

Gunshot Forward SpatterGunshot Forward Spatter

• Arises from exit wound• Passes forwards in same direction as shot• More copious than back-spatter• Can be seen at any range of fire• Seen on nearby surfaces, objects, persons

– especially on wall behind victim

62

Forward spatter (5 ms after bullet impacted at 1000 f/s)

2.5 cm

blood soaked target

bullet

63

6” ruler

Forward spatter onto target placed 15 cm behind point of HV bullet impact (bullet passing towards screen) 1

64

Forward spatter (closer view)65

Forward spatter (closest view)

5 mm

66

Wipe PatternsWipe Patterns• Object moves through a wet bloodstain• Feathered edge suggests direction

67

Transfer PatternsTransfer Patterns

• Wet, bloodied object contacts a secondary surface

• Transfer from:– hand, fingers

– shoes, weapon

– hair

• Transfer to:– walls, ceilings

– clothing, bedding

• Produces mirror-image of bloodied object

68

Transfer from hair (hair-swipe) 1

69

Transfer from hair (hair-swipe) 2

70

Flow PatternsFlow Patterns• Blood flows horizontally & vertically• Altered by contours, obstacles• Often ends in pool

71

Flow pattern72

Trapped!

73

Stabbing 1

74

Stabbing 275

Blood flow on shirt

Horizontally to R side

76

Pattern on shirt77

Bloodspots on trousers78